The present invention relates to substrates for use in the preparation of printed circuits and the like. In particular, the present invention is directed to substrate materials for use in the preparation of electrical circuits comprising conductive inks of the type disclosed, for example, in co-pending U.S. application Ser. No. 07/769,892, now U.S. Pat. No. 5,376,403.
Printed circuits are typically prepared by adhering conductive traces which form an electrical interconnect pattern onto a suitable substrate. Commonly-employed substrate materials have included epoxy-glass laminate, paper-phenolic laminate, polyimide-glass laminate, flexible polyimide films, and injection molded plastics such as liquid crystal polymers and Ryton.RTM. (available from Phillips 66, Bartlesville, Okla.). Copper foil has most successfully been used to form conductive traces on these substrates, in particular because of its high electrical conductivity and the strong bond formed when the copper foil is laminated to the substrates.
More recently, electrically conductive ink compositions have been developed for use in preparing conductive traces. As such conductive ink compositions may be applied using various printing techniques which offer significant advantages in economy and efficiency, considerable attention has been devoted to various formulations. In many cases, however, the conductive ink compositions heretofore developed have not exhibited adequate adhesion to the more commonly-employed substrate materials noted above, and thus printed circuits prepared using the known conductive ink compositions have not exhibited adequate reliability or durability for many uses.
Co-pending U.S. patent application Ser. No. 07/769,892 filed Oct. 1, 1991, now U.S. Pat No. 5,376,403, the entire disclosure of which is hereby incorporated by reference, describes electrically conductive compositions comprising a solder powder, a chemically protected cross-linking agent with fluxing properties, and a reactive monomer or polymer. Such compositions including in addition a high melting metal powder (for example, copper) and optionally a resin are particularly suitable for use as conductive inks for preparation of printed circuits. While the compositions of U.S. Pat. No. 5,376,403 provide bulk electrical conductivities approaching that of solid copper and highly corrosion resistant final products with resistance to degradation at high temperatures and relative humidities, some of these compositions also do not exhibit entirely adequate adhesion properties when applied to many of the traditional substrate materials. As the above-noted substrate materials have highly desirable mechanical and electrical properties (in particular, high strength, light weight, good high temperature stability and flexibility) which are important for preparation of useful printed circuits and are of a relatively low cost, it would be highly advantageous if substrates comprising these materials could be employed in combination with conductive ink compositions.
Accordingly, it is an object of the present invention to provide novel substrate materials which exhibit both the desirable bulk properties of conventional substrates and surface properties suitable for formation of strong adhesive bonds with conductive ink compositions.